High power turbo generators for the generation of electrical energy have evolved in the perspective of increasing unitary power, which, in turn, requires to increase electrical currents, and consequently requires to increase stator cooling.
Generally, the stator of a turbo generator comprises: a cylindrical core, which extends along a first longitudinal axis and comprises a plurality of axial cavities and two opposite headers; connection terminals of the turbo generator; a plurality of electrical windings, which are split into groups and which extend along paths defined in part in the axial cavities and in part at the headers; the electrical windings of each group being isopotential and connected in parallel between a pair of terminals.
A known stator of a three-phase turbo generator comprises six terminals (three of which are connected to earth and three of which are connected to the electrical energy distribution main), nine electrical windings which are split into three groups each comprising three isopotential electrical windings connected in parallel between a pair of terminals; seventy-two cavities, each of which is occupied at the same time by two different portions of electrical windings. The electrical windings have straight segments accommodated in the cavities and connection segments, which are arranged at the headers and which have the function of connecting together the straight segments arranged in different axial cavities and some straight segments to the terminals.
Considering that, according to the wiring diagram of the stator described above, each axial cavity is occupied at the same time by two different electrical windings and that each electrical winding presents a path essentially identical to the other electrical windings, each electrical winding presents sixteen straight segments, which are arranged at corresponding axial cavities, and a plurality of connection segments, which are adapted to connect the straight segments to each other and to the terminals, and are arranged at the headers.
The connection segments determine a considerable axial dimension at the header of the stator, above all considering that the electrical windings are generally defined by bars which must be maintained spaced apart one from the other. Furthermore, the axial dimension of the stator is increased by the wiring configuration followed by the electrical windings: indeed, in an electrical winding it is often necessary to connect together two straight segments arranged in diametrically opposite axial cavities.
The technical solution of forming isopotential electrical windings between a pair of terminals, rather than a single electrical winding between a pair of terminals, allows to decrease the current value in the single isopotential electrical windings; to increase the cooling surface; and to reach higher unitary powers with respect to traditional electrical windings and for a given ventilating gas. The currently known solutions envisage the formation of two or three isopotential electrical windings connected in parallel between each pair of terminals.
The stators which adopt this type of solution, i.e. of fractioning the electrical windings of the stator, in addition to the aforementioned drawback of the axial dimensions due to the high number of connection segments at the headers, present the drawback of overloading with electrical current the connection zones of the electrical windings to the terminal pair to which they lead.
In order to obviate to this drawback, each isopotential electrical winding is connected to a respective terminal by means of a ventilated connection device which, in turn, determines a further increase of axial dimensions.